While of broader applicability, for example in the field of highway vehicles where use of certain features of the invention can reduce lateral scrubbing of tires as well as lessening the width of the roadway required for negotiating curves, my invention is especially useful in railway vehicles and particularly railway trucks having a plurality of axles. Accordingly, and for exemplary purposes, the invention will be illustrated and described with specific reference to railway rolling stock.
The axles of the railway trucks now in normal use remain substantially parallel at all times (viewed in plan). A most important consequence of this is that the leading axle can not assume a position radial to a curved track, and the flanges of the wheels strike the curved rails at an angle, causing objectionable noise and excessive wear of both flanges and rails.
Much consideration has been given to the avoidance of this problem, notably the longstanding use of wheels the treads of which have a conical profile. This expedient has assisted the vehicle truck to negotiate very gradual curves. However, as economic factors have led the railroads to accept higher wheel loads and operating speeds, the rate of wheel and rail wear becomes a major problem. A second serious limitation on performance and maintenance is the result of excessive, and even violent, oscillation of the trucks at high speed on straight track. In such "nosing", or "hunting", of the truck the wheelsets bounce back and forth between the rails. Above a critical speed hunting will be initiated by any track irregularity. Once started, the hunting action will often persist for miles with flange impact, excessive roughness, wear and noise, even if the speed be reduced substantially below the critical value.
In recent efforts to overcome this curving problem, yaw flexibility has been introduced into the design of some trucks, and arrangements have even been proposed which allow wheel axles of a truck to swing and thus to become positioned substantially radially of a curved track. However, such efforts have not met with any real success, primarily because of lack of recognition of the importance of providing the required lateral restraint, as well as yaw flexibility, between the two wheelsets of a truck, to prevent high speed hunting.
For the purposes of this invention, yaw stiffness can be defined as the restraint of angular motion of wheelsets in the steering direction, and more particularly to the restraint of conjoint yawing of a coupled pair of wheelsets in a truck. The "lateral" stiffness is defined as the restraint of the motion of a wheelset in the direction of its general axis of rotation, that is, across the line of general motion of the vehicle. In the apparatus of the invention, such lateral stiffness also acts as restraint on differential yawing, of a coupled pair of wheelsets.
The above-mentioned general problems produce many particular difficulties all of which contribute to excessive cost of operation. For example, there is deterioration of the rail, as well as widening of the gauge in curved track. In straight track the hunting, or nosing, of the trucks causes high dynamic loading of the track fasteners, and of the press fit of the wheels on the axles, with resultant loosening and risk of failure. A corresponding increased cost of maintenance of both trucks and cars also occurs. As to trucks, mention may be made, by way of example, to flange wear and high wear rates of the bolster and of the surfaces of the side framing and its bearing adapters.
As to cars, there occurs excessive center plate wear, as well as structural fatigue and heightened risk of derailment resulting from excessive flange forces. The effects on power requirements and operating costs, which result from wear problems of the kinds mentioned above, will be evident to one skilled in this art.
In brief, the lack of recognition of the part played by yaw and lateral stiffness has led to: (a) flange contact in nearly all curves; (b) high flange forces when flange contact occurs; and (c) excessive difficulty with lateral oscillation at high speed. The wear and cost problems which result from failure to provide proper values of yaw and lateral stiffness, and to control such values, will now be understood.